This invention relates generally to the production of phosphor screens for shadow mask type color picture tubes and particularly to a system and method for determining the exposure time required to produce such screens under conditions in which the intensity of the exposing light transmission characteristics of the shadow mask vary.
A color picture tube includes a screen composed of triads of different phosphor which emit different colored light when excited by electrons. Typically, the system is composed of alternating stripes of phosphors which respectively emit red, green and blue light. Positioned between the screen and the electron gun from which the electrons emanate is an apertured color selection electrode, commonly called a shadow mask. The shadow mask assures that the electron beams excite phosphor stripes of the proper color.
During the production of the phosphor screen the entire inside surface of the panel is coated with one of the phosphors mixed in a photosensitive material. The shadow mask is then inserted into the panel and the assembly is placed on a lighthouse which contains a light source. Light from the light source passes through the apertures in the shadow mask and exposes some of the phosphor. The shadow mask is then removed and the unexposed phosphor is washed away leaving only the exposed phosphor. This process is then repeated for the remaining two colors of phosphors.
U.S. application Ser. No. 267,750 entitled "System And Method For Controlling The Exposure Of Color Picture Tube Phosphor Screens" filed on even date herewith by William R. Kelly and Ernesto J. Alvero and assigned to RCA Corporation, the assignee of the instant invention, discloses a system for controlling the exposure time-intensity multiple of the lighthouse which is used to automatically expose the phosphors on kinescope faceplate panels of differing sizes.
U.S. application Ser. No. 267,991, now U.S. Pat. No. 4,370,036, entitled "System And Method For Intermittently Moving A Picture Tube Panel On A Lighthouse" filed on even date herewith by William R. Kelly and Ernesto J. Alvero and assigned to RCA Corporation, the assignee of the instant invention, discloses a system for intermittently moving a faceplate panel along a lighthouse during the exposure of the phosphors.
Both systems disclosed in the referenced patent applications require the accurate input of the light transmission characteristics of the shadow mask contained within the panels being exposed. Accordingly, irrespective of whether or not the light transmission characteristics of the shadow mask are input to the systems by use of automatic input means, such as a programmed computer or a microprocessor, or manually set into the system by the utilization of thumb wheel switches on the panel of the system, the intended operation of both the systems is dependent upon receiving accurately determined light transmission characteristics of the shadow mask contained within the faceplate panel being exposed.
Additionally, because the system described in the referenced applications are intended for use on assembly lines in which faceplate panels of varying sizes are selected at random, the light transmission characteristics of the shadow masks within the individual panels must be accurately categorized and input to the processing systems.
The instant invention is directed to a system for determining the light transmission characteristics of color picture tube shadow masks of varying sizes and types and for calculating the time required to properly expose the phosphor screens associated with such shadow masks.